在接收到SIGTERM之后，python进程如何在等待信号量时优雅地退出？

Question

我有一个Python进程，它使用多处理模块生成5个其他Python进程。让我们调用父进程P0和其他P1-P5。要求是，如果我们向P0发送一个SIGTERM，它应该首先关闭P1到P5，然后退出自己。

问题是P1和P5在等待信号量。因此，当我向这些进程发送SIGTERM时，它们调用信号处理程序并退出。但是，由于他们在等待信号量，他们抛出一个异常。是否有任何方法在退出之前捕获该异常，以便P0 to P5可以进行优雅的退出？

回溯：

Traceback (most recent call last):
  File "/usr/lib64/python2.7/multiprocessing/process.py", line 258, in _bootstrap
Traceback (most recent call last):
Process Process-2:
  File "/usr/lib64/python2.7/multiprocessing/process.py", line 258, in _bootstrap
Traceback (most recent call last):
self.run()
File "/usr/lib64/python2.7/multiprocessing/process.py", line 114, in run
self._target(*self._args, **self._kwargs)
Process Process-5:
Traceback (most recent call last):
File "/usr/lib64/python2.7/multiprocessing/process.py", line 258, in _bootstrap
  self.run()
File "/usr/lib64/python2.7/multiprocessing/process.py", line 114, in run
  self._target(*self._args, **self._kwargs)
File "/opt/fireeye/scripts/mip/StaticAnalysisRunner.py", line 45, in run
  qsem.acquire()

Answer 1

您可以安装一个信号处理程序，该处理程序抛出一个异常，然后在子进程中捕获该异常，以便优雅地处理出口。

下面是一个脚本的示例，它在子进程的信号量中等待，在发送SIGTERM时优雅地终止。

#!/usr/bin/env python

import signal
import time
import multiprocessing

class GracefulExit(Exception):
    pass


def signal_handler(signum, frame):
    raise GracefulExit()


def subprocess_function():
    try:
        sem = multiprocessing.Semaphore()
        print "Acquiring semaphore"
        sem.acquire()
        print "Semaphore acquired"

        print "Blocking on semaphore - waiting for SIGTERM"
        sem.acquire()
    except GracefulExit:
        print "Subprocess exiting gracefully"


if __name__ == "__main__":

    # Use signal handler to throw exception which can be caught to allow
    # graceful exit.
    signal.signal(signal.SIGTERM, signal_handler)

    # Start a subprocess and wait for it to terminate.
    p = multiprocessing.Process(target=subprocess_function)
    p.start()

    print "Subprocess pid: %d" % p.pid

    p.join()

此脚本的示例运行如下：

$ ./test.py 
Subprocess pid: 7546
Acquiring semaphore
Semaphore acquired
Blocking on semaphore - waiting for SIGTERM
----> Use another shell to kill -TERM 7546
Subprocess exiting gracefully

没有来自子进程的追溯，流程显示子进程以优雅的方式存在。这是因为SIGTERM被子进程信号处理程序捕获，该处理程序抛出一个正常的Python异常，该异常可以在进程内处理。